Why scan photos at lower resolution than possible?

[Mike77]

Hi,

I've read a couple of the posts on this forum but it's not clear to me why it is better to scan old photo's on a lower resolution. I'm trying to find out what way is best to scan my old photo's. Storage isn't a direct problem. I just want to make te best possible scans in tif format, so that future generations have the best data to work with and to reproduce the immages.

Is there a reason (except storage, etc?) to scan normal size pictures at lower resolution then possible? I'm using an Epson Perfection V550 Photo.

[juhok]

As a rule of thumb most prints have 300 DPI resolution or less. I would recommend 2x oversampling -> 600 DPI scans for archive. Oversampling too much will give more dirt, dust and scratches but no image information.

Some old analog prints will have more than 300 DPI worth of information if they are exceptional.

[Mike77]

Juhok, thanks for your reply.

Some old picture? Is there a way to find out which? Most of the pictures are pretty recent (1950-2010), but Some are much older. Old portrayts of grand grand parents etc.

So 600dpi woud be good enough for all normal pictures, but is there a way to check this (see this?)

[juhok]

If the process was 100% analog it could have more than 300 DPI. At some point print shops moved to digital workflows even for analog film. Film -> development -> scan -> print. These digital workflows are pretty much capped at 300 DPI because of technological limitations.

Anything from 1950 will be pure analog. If you have very well made (good lens, good film, good print/paper) from 1950's
then I would just judge it case by case OR choose a value that covers all possibilities. I have used 1200 DPI in this case.

edit: If we're hunting for 'the best' I would recommend reading about wet scanning techniques.

In my experience medium or large format contact prints have often >300 DPI. Old prints made this way are direct 1:1 prints from medium format negatives to the print paper without enlargement machine. The prints made this way usually are pretty small in size but contain a lot of information. YMMV.

[kpmedia]

There are several factors to consider. It's not a simple binary question.

1. The optical resolution of the scanner.
2. The quality of interpolation past the optical, and how it fairs against other methods. Not just simple bicubic or biliear (ala Photoshop), but fractal upsizing.
3. The source image media -- usually negative vs. print.
4. The source image quality.
5. The source image size.
6. The destination image size.

Here's an example:

Right now, today, I'm scanning an old 1950s photo at the request of a family member.

It's a B&W 4x4 print, and is glued into a photo album. It's not 100% perfect, but decent. There is some warping of the image due to aged glue on the back, and some minor crud has dented the image. And the usual dust, lint, etc. (Note that these tiny errors were invisible to the eye, and were only seen when magnified in a scan.)

The original print is pretty blah, lacking any real contrast.

He wants a 12" x 12" print. (Not only that, but he wants me to colorized the B&W. Which I can do quite well.)

The source image is probably not even 300dpi in quality. (I worked for newspapers pre-, during phase-in, and post-digital. We'd scan negatives at about 2000dpi, and downsize those to 200dpi for press. This image closely matches 200dpi quality from my old tearsheets.)

I scanned his photo at 300, 600, 1200, 2400, 3200, and 4800.

The quality of the scanner (Epson V600) is somewhat blurrier than the source at 300dpi. I believe it's from the speed of the scanner -- it moves too fast at 300dpi! At 600dpi, all details were retained. At 1200, 2400, 3200 and 4800 it appeared the same.

However, starting at 2400, the image scan quality was not as good as what I could achieve with a 1200dpi scan, and using some quality Photoshop work (or third-party filters like On1 Perfect Resize, the fractal resizer).

Every situation will work out a bit differently. Examples:
- An old Polaroid usually will not look at different above 600dpi.
- Most large 8x10 images are equally blurry, but can look better when scanned at 1200dpi and shrunk to 300/600dpi (also assuming final image will be displayed smaller, either print or web).
- A 35mm fine-grain negative, however, looks best when scanned at 4000dpi.

There's not a single answer.